1. different viewing perspectives
1.1. longitudinal section
1.1.1. cutting along the length of the cell
1.2. transverse section
1.2.1. cutting across the length of the cell
2. are the
2.1. building blocks of life
2.1.1. too small to be seen by the naked eye
2.1.1.1. so we use a
2.1.1.1.1. light microscope
2.1.1.1.2. electron microscope
2.2. simplest units that exhibit characteristics of life
3. types
3.1. typical plant cell
3.1.1. has
3.1.1.1. cell wall
3.1.1.1.1. made of cellulose
3.1.1.1.2. fully permeable
3.1.1.1.3. absent in animal cells
3.1.1.2. chloroplasts
3.1.1.2.1. oval structures containing chlorophyll which absorbs light energy to carry out photosynthesis
3.1.1.3. tonoplast
3.1.1.3.1. encloses
3.1.1.4. vacuole
3.1.1.4.1. store substances withing the cell
3.2. typical animal cell
3.2.1. has
3.2.1.1. nucleus
3.2.1.1.1. controls cell activities, e.g.
3.2.1.1.2. essential for cell division
3.2.1.1.3. contains
3.2.1.2. cell surface membrane
3.2.1.2.1. aka plasma membrane
3.2.1.2.2. partially permeable
3.2.1.2.3. controls the substances entering and leaving the cell
3.2.1.3. cytoplasm
3.2.1.3.1. site of most cell activities
3.2.1.3.2. contains specialised membrane-bound structures calles organelles
3.2.1.3.3. contains
3.3. specialised cells
3.3.1. what is differentiation?
3.3.1.1. process by which a cell becomes specialised for a specific function
3.3.2. examples
3.3.2.1. red blood cell (RBC)
3.3.2.1.1. haemoglobin in cytoplasm of RBC -> transports oxygen from lungs to all parts of the body
3.3.2.1.2. has no nucleus -> can carry more haemoglobin and thus more oxygen
3.3.2.1.3. circular biconcave shape (thinner central portions) -> increases surface area to volume ratio -. increases rate of diffusion of oxygen into and out of the cell
3.3.2.1.4. flexible and elastic -> able to turn bell-shaped to allow the cell to squeeze through tiny capillaries
3.3.2.2. xylem vessels
3.3.2.2.1. long hollow tubes from the root to the leaves
3.3.2.2.2. narrow and do not have cross walls or protoplasm to obstruct water and mieral salt flow (reduce resistance) through the lumen
3.3.2.2.3. walls thickened with lignin -> prevent the vessel from collapsing
3.3.2.2.4. vessels clumped together -> making lumen even stronger, keeping the plant upright
3.3.2.3. root hair cell
3.4. long & narrow protrusion -> increases surface area to volume ratio, allowing the root hair cell to absorb water and mineral salts at a faster rate
3.5. differences
3.5.1. plant cell
3.5.1.1. cell wall present
3.5.1.2. chloroplast present
3.5.1.3. centrioles absent
3.5.1.4. a large central vacuole
3.5.2. animal cell
3.5.2.1. cell wall absent
3.5.2.2. chloroplast absent
3.5.2.3. centrioles present (involved in cell division)
3.5.2.4. numerous small vacuoles
4. cells
4.1. tissue
4.1.1. organ
4.1.1.1. organ system
4.1.1.1.1. organism
4.1.1.1.2. several related organs working together to carry out a particular function
4.1.1.1.3. e.g. digestive system, respiratory system
4.1.1.2. different tissues working together to carry out a specific function
4.1.1.3. different tissues may be untied to form an organ
4.1.1.4. e.g. stomach: digests food and is made up of glandular tissue, muscular tissue and nervous tissue
4.1.1.5. e.g. leaf: made up of several types of tissues, namely the mesophyll tissue, xylem tissue & phloem tissue
4.1.2. a group of similar cells which work together to perform a certain function
4.1.3. cells of the same type
4.1.3.1. e.g. muscle & epithelial tissue in animals, epidermis & mesophyll tissue in plants
4.1.4. complex tissues are tissues made up of several different cell types
4.1.4.1. e.g. nervous tissue (sensory neurones, relay neurones, motor neurones) & blood tissue (RBCs, WBCs, platelets, plasma) in animals, vascular tissue (xylem & phloem, where phloem consists of sieve tubes, sieve plate & companion cells) in plants
4.2. specialised for a specific function
5. Molecular Genetics
5.1. deoxyribonucleic acid (DNA)
5.1.1. organisation
5.1.1.1. each DNA molecule consists of two anti-parallel strands (the two strands run in opposite directions) twisted around each other to form a double helix
5.1.1.2. a molecule of DNA is wrapped around proteins (histones) to form a single chromatin thread
5.1.1.3. during cell division, the chromatin threads coil & condense more tightly to form chromosomes inside the cell nucleus
5.1.2. what is DNA?
5.1.2.1. molecule that carries genetic information
5.1.2.2. made up of two anti-parallel polynucleotide strands
5.1.2.2.1. bases on one strand form bonds with the bases on the other strand according to the rule of complementary base pairing
5.1.2.2.2. one coding strand and one non-coding strand
5.1.2.3. double helix structure
5.1.2.4. made up of nucleotides
5.1.2.4.1. which are made up of
5.1.2.4.2. can be joined together to form polynucleotides
5.2. genes
5.2.1. a segment of DNA that codes for the synthesis of a single polypeptide
5.2.1.1. determined by the nucleotide sequence in the gene
5.2.1.2. 3 nucleotides in a gene form a codon and each codon codes for one amino acid
5.2.1.2.1. total of 64 (4 to the power of 3) different possible codons
5.2.1.2.2. genetic code states which amino acid each codon codes for
5.2.1.2.3. important pointers
5.2.1.3. in ribonucleic acid (RNA), thymine is replaced by uracil
5.2.2. what happens when the nucleotide sequence in a gene is altered?
5.2.2.1. termed as a gene mutation
5.2.2.2. gene mutation may or may not lead to a change in protein product
5.2.2.2.1. e.g. changing GUU to GUC will not change the product formed but changing GUU to AUU will change the product formed
5.2.2.3. change in protein may or may not lead to an observable phenotype
5.2.2.4. e.g. of gene mutations
5.2.2.4.1. albanism: mutation in the the gene causes an absence or defect in the enzyme that produces the pigment melanin
5.2.2.4.2. sickle-cell anaemia: mutation in the gene causes the protein product to differ from the normal protein by a single amino acid, causing RBC to become sickle
5.2.2.5. DNA -> amino acid (polypeptide) -> folds to form a protein
5.2.3. how proteins are made from genes
5.2.3.1. DNA to messenger RNA (mRNA): process - transcription, location - nucleus
5.2.3.1.1. process
5.2.3.1.2. biological molecules involved
5.2.3.1.3. DNA is the template for mRNA synthesis
5.2.3.2. mRNA to polypeptide: process - translation, location - cytoplasm
5.2.3.2.1. process
5.2.3.2.2. mRNA is the template for polypeptide synthesis
5.2.4. comparison between DNA and RNA molecules
5.2.4.1. DNA
5.2.4.1.1. responsible for storing and transferring genetic information
5.2.4.1.2. deoxyribose sugar
5.2.4.1.3. double-stranded
5.2.4.1.4. nitrogenous bases: guanine, cytosine, adenine, THYMINE
5.2.4.1.5. bigger; longer chain of nucleotides
5.2.4.1.6. ratios of A:T & G:C = 1:1
5.2.4.1.7. always present
5.2.4.2. RNA
5.2.4.2.1. directly codes for amino acids and acts as a messenger between DNA and ribosomes to make proteins
5.2.4.2.2. ribose sugar
5.2.4.2.3. single-stranded
5.2.4.2.4. nitrogenous bases: guanine, cytosine, adenine, URACIL
5.2.4.2.5. smaller; shorter chain of nucleotides
5.2.4.2.6. no fixed ratio
5.2.4.2.7. only made when needed
5.3. transferring genes between organisms
5.3.1. genetic engineering refers to the manipulation of an organism's genetic material
5.3.2. involves the transfer of genes from one organism to another
5.3.3. done by the use of a vector molecule
5.3.3.1. a vector molecule is a molecule that is used to carry a gene or genes from one organism to another
5.3.3.2. plasmids (circular DNA) from bacteria are commonly used as vectors
5.3.4. process
5.3.4.1. isolate the desired gene
5.3.4.1.1. desired gene is 'cut' using a restriction enzyme, creating complementary sticky ends at the ends of the desired gene
5.3.4.1.2. the bacterial plasmid is 'cut' by the same restriction enzyme as the desired gene, creating complementary sticky ends in the bacterial plasmid as well
5.3.4.2. insert the gene into the vector DNA
5.3.4.2.1. the desired gene is inserted into the bacterial plasmid
5.3.4.2.2. held together using DNA ligase which acts as a glue for the sticky ends of the desired gene and the bacterial plasmid
5.3.4.2.3. forms a recombinant plasmid
5.3.4.3. insert the recombinant plasmids into bacteria
5.3.4.3.1. the recombinant plasmid is too large to fit through the cell membrane of the bacterium
5.3.4.3.2. the recombinant plasmid and the bacterium are given a heat shock
5.3.4.3.3. the pores on the cell surface membrane open temporarily for the plasmid to enter
5.3.4.3.4. forms a transgenic bacterium
5.3.5. producing human insulin
5.3.5.1. background: type 1 diabetes is caused by the inability of the islet of Langerhans to produce sufficient insulin
5.3.5.2. mass production of insulin for type 1 diabetes patients was made possible through the use of genetic engineering
5.3.5.3. the human insulin gene is transferred to bacterial cells that are able to express th gene
5.3.5.4. the product (insulin) can then be harvested
5.3.6. large scale production of human insulin
5.3.6.1. transgenic bacteria need to be burst open in order to extract the human insulin that is produced in bacteria
5.3.6.2. in order to produce large amounts of human insulin, large amounts of transgenic bacteria needs to be cultured
5.3.6.3. done through the use of large sterile containers called fermenters
5.3.6.4. essential components of a fermenter
5.3.6.4.1. nutrient broth
5.3.6.4.2. cooling kacket
5.3.6.4.3. pH controller
5.3.6.4.4. aeration system
5.3.7. other applications of genetic engineering
5.3.7.1. creation of transgenic plants that are resistant to
5.3.7.1.1. herbicides
5.3.7.1.2. pests
5.3.7.2. gene therapy: healthy genes from a person can be transferred to the cells of another person with defective genes
5.3.7.3. note: genes can be transferred between organisms of different species and between organisms of the same species
5.3.7.3.1. e.g. transfer of a pest-resistant gene from wild wheat plants to common wheat plants that are grown as crop
5.3.8. selective breeding vs genetic engineering
5.3.8.1. selective breeding
5.3.8.1.1. organisms involved in selective breeding must be closely related or of the same species
5.3.8.1.2. there is a possibility that defective genes will be transmitted to the offspring
5.3.8.1.3. slow process that involves several generations
5.3.8.1.4. less efficient as organisms grow more slowly and may require more food
5.3.8.2. genetic engineering
5.3.8.2.1. genes from an organism can be inserted into non-related species or different species
5.3.8.2.2. selection of genes before transfer eliminates risk of transferring a defective gene
5.3.8.2.3. a process which uses individual cells that reproduce rapidly in a small container in a laboratory
5.3.8.2.4. more efficient as transgenic organisms grow faster and may require less food
5.4. effects of genetic engineering on society
5.4.1. advantages
5.4.1.1. low cost production of medicines
5.4.1.1.1. drugs such as human insulin become more affordable
5.4.1.2. production of crops that grow in extreme conditions
5.4.1.2.1. farmers are able to grow crops in environmental conditions that are unfavourable for cultivating most crops
5.4.1.3. development of pesticide-resistant crops
5.4.1.3.1. use of costly pesticides that may damage the environment is reduced
5.4.1.4. development of foods designed to meet specific nutritional goals
5.4.1.4.1. nutritional quality of food is improved
5.4.2. disadvantages
5.4.2.1. economic hazards
5.4.2.1.1. if prices of genetically (GM) crop seeds are not regulated, poorer farmers may not benefit from the technology while their richer competitors will continue to get richer through the technology
5.4.2.2. environmental hazards
5.4.2.2.1. GM crops that produce insect toxins may result in the loss of insect biodiversity
5.4.2.3. social and ethical hazards
5.4.2.3.1. GM may lead to class distinctions and religious disputes
5.4.2.4. health hazards
5.4.2.4.1. genes that code for antibiotic resistance may be accidentally incorporated into bacteria that cause human diseases